1. Field of the Invention
The present invention relates generally to a tuning fork type piezoelectric resonator in which a piezoelectric substrate is provided with a slit and tuning fork arm portions are formed on both sides of the slit, and more particularly, to a tuning fork type piezoelectric resonator provided with a structure for preventing leakage of vibration from tuning fork arm portions.
2. Description of the Prior Art
One example of a conventional tuning fork type piezoelectric resonator will be described with reference to FIG. 2.
A tuning fork type piezoelectric resonator 1 is constructed using a rectangular piezoelectric substrate 2. A first slit 5 is formed so as to extend inward from the center of one edge 2a of the piezoelectric substrate 2. Second .and third slits 4 and 5 are similarly formed on both sides of the first slit 3 so as to extend inward from the edge 2a. Piezoelectric tuning fork arm portions 6 and 7 are formed on both sides of the first slit 3 by thus forming the second and third slits 4 and 5 on both sides of the first slit 3. Resonance electrodes 8 and 9 are formed on both major surfaces of the piezoelectric substrate 2 in a region around the innermost part of the first slit
In FIG. 2, electrodes formed on the reverse surface of the piezoelectric substrate 2 are illustrated with the lower surface of the piezoelectric substrate 2 being projected downward as shown.
The tuning fork type piezoelectric resonator 1 is so constructed that a region where the resonance electrodes 8 and 9 are opposed to each other is vibrated by applying a voltage from terminal electrodes 10a and 10b connected to the resonance electrodes 8 and 9, so that the piezoelectric tuning fork arm portions 6 and 7 are vibrated in a tuning fork type mode of vibration.
In the tuning fork type piezoelectric resonator 1, the above described second and, third slits 4 and 5 are formed in the rectangular piezoelectric substrate 2 so as not to prevent vibration from the tuning fork arm portions 6 and 7. When the tuning fork type piezoelectric resonator 1 is fixed to a circuit board or the like by solder or the like, however, the resonance characteristics of the tuning fork type piezoelectric resonator 1 may, in some cases, be largely varied from the original resonance characteristics.
Therefore, the inventors of the present application have analyzed the vibrating state of the tuning fork arm portions 6 and 7 in the tuning fork type piezoelectric resonator 1 using the finite element method, thereby to recognize that not only the tuning fork arm portion 7 but also other portions of the piezoelectric substrate are displaced. More specifically, it is recognized that even a piezoelectric substrate portion 2a outside of the third slit 5 and a piezoelectric substrate portion 2d on the side of an edge 2b opposed to the edge 2a are displaced as the tuning fork arm portion 7 is vibrated.
In the conventional tuning fork type piezoelectric resonator 1, therefore, it is found that the piezoelectric substrate portions 2c and 2d which are portions fixed to a circuit board or the like are displaced by leakage of vibration from the tuning fork arm portions 6 and 7 positively displaced. As a result, when the piezoelectric substrate portions 2c and 2d are fixed to the circuit board or the like, the vibration is restrained in the piezoelectric substrate portions 2c and 2d. Accordingly, the vibrating state of the tuning fork arm portions 6 and 7 is affected by the above described fixing, so that the resonance characteristics of the tuning fork type piezoelectric resonator 1 are forced to be degraded.